Compact system for coupling rf power directly into rf linacs

ABSTRACT

A system and associated method are described for depositing high-quality films for providing a nanolayered coating on a three-dimensional surface. The system includes a magnetic array comprising multiple sets of magnets arranged to have Hall-Effect regions that run lengthwise along a sputter target. The system further includes an elongated sputtering electrode material tube surrounding the magnetic array comprising multiple sets of magnets arranged to have Hall-Effect regions that run lengthwise along the sputter target. During operation, the system generates and controls ion flux for direct current high-power impulse magnetron sputtering. During operation logic circuitry issues a control signal to control a kick pulse property of a sustained positive voltage kick pulse taken from the group consisting of: onset delay, amplitude and duration.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of, and claims the priorityof, U.S. application Ser. No. 15/803,320, filed Nov. 3, 2017 (U.S. Pat.No. 10,624,199), entitled “A COMPACT SYSTEM FOR COUPLING RF POWERDIRECTLY INTO RF LINACS,” which is a non-provisional of U.S. ProvisionalApplication Ser. No. 62/416,900, filed Nov. 3, 2016, entitled “A COMPACTSYSTEM FOR COUPLING RF POWER DIRECTLY INTO RF LINACS,” the contents ofeach of which are expressly incorporated herein by reference in theirentirety, including any references therein.

This application is a continuation-in-part of, and claims the priorityof, U.S. application Ser. No. 16/006,357, filed on Jun. 12, 2018,entitled “PULSED POWER MODULE WITH PULSE AND ION FLUX CONTROL FORMAGNETRON SPUTTERING,” which is a non-provisional of U.S. ProvisionalApplication Ser. No. 62/518,362, filed Jun. 12, 2017, entitled “PULSEDPOWER MODULE WITH PULSE AND ION FLUX CONTROL FOR MAGNETRON SPUTTERING,”the contents of each of which are expressly incorporated herein byreference in their entirety, including any references therein.

This application is a continuation-in-part of, and claims the priorityof, U.S. application Ser. No. 16/801,002, filed Feb. 25, 2020, andentitled “METHOD AND APPARATUS FOR METAL AND CERAMIC NANOLAYERING FORACCIDENT TOLERANT NUCLEAR FUEL, PARTICLE ACCELERATORS & AEROSPACELEADING EDGES,” which is a non-provisional of U.S. Provisional PatentApplication No. 62/810,230, filed on Feb. 25, 2019, entitled “METHOD ANDAPPARATUS FOR METAL AND CERAMIC NANOLAYERING FOR ACCIDENT TOLERANTNUCLEAR FUEL,” the contents of each of which are expressly incorporatedherein by reference in their entirety, including any references therein.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT

This work has been supported by the U.S. Defense Advanced ResearchProjects Agency (DARPA), under contract HR0011-15-C-0072. The views,opinions, and/or findings expressed are those of the authors and shouldnot be interpreted as representing the official views or policies of theDepartment of Defense or the U.S. Government.

TECHNICAL FIELD

The disclosure generally relates to injecting power into acceleratordevices, and more particularly to relatively compact high-power radiofrequency linear accelerator (RF LINAC) systems.

BACKGROUND OF THE INVENTION

High-power RF cavities, such as those found in an RF LINAC, require notonly tremendous RF powers (on the order to 10's to 100's of kW andabove), but also a vacuum environment to prevent arcing and sparkingwithin the RF cavity due to the intense electric fields associated withsuch high powers. The RF power needed to reach a specific electric fieldwithin the resonant cavity is governed by the quality factor (Q) whichis integral energy stored divided by energy lost per cycle. For resonantRF cavities, the formula reduces to

$Q = {\frac{\sqrt{\frac{L}{C}}}{R_{surface}} = \left( \frac{\Delta \omega}{\omega_{o}} \right)^{- 1}}$

since the RF energy propagates along the surface and is a function ofthe surface resistance

$R_{surface} = \frac{1}{{Conductivity} \times {Skin}\mspace{14mu} {Depth}}$

that is proportional to the square root of RF frequency. Higher qualityfactor leads to higher efficiencies, higher achievable voltages andaccelerating gradients. However, there are engineering tradeoffs incavity design and operation since electrical skin depths are on theorder of microns for GHz frequencies. RF cavities are typicallyelectroplated with copper for lower surface resistance or constructedout of solid blocks of base material for room-temperature cavities.

Typically, RF power is coupled into a high-power RF cavity via awaveguide and a hermetic RF window. This approach, while viable at highpower LINAC applications, requires additional hardware, which increasesthe cost, size and complexity of compact high power RF LINAC systems. Analternative approach to the one described above is to couple RF powerdirectly into the RF cavity via an RF amplifier assembly mounted on, andwith an output stage coupled directly to, the RF cavity. This approachis described in Swenson, U.S. Pat. No. 5,084,682. However, the inclusionof the entire vacuum tube (and its associated tuning elements) withinthe vacuum envelope has led to an inability to operate at high powersdue to processes such as multipactoring. For this reason, as much aspossible of the RF and biasing circuitry needs to be at atmosphericpressure. In addition to this constraint, problems arise in thestructure described in Swenson due to high powers dissipated both in theantenna and in the anode of the vacuum tube if these structures are notactively cooled. Swenson's approach to mounting the RF amplifier in ahigh power RF LINAC is further complicated by a vacuum tube anodecommonly being held at high voltage, which necessitates the carefulselection of a coolant.

SUMMARY OF THE INVENTION

A system is provided for depositing high-quality films for providing ananolayered coating on a three-dimensional surface of an RF acceleratorand associated superconducting cavities. The system includes a magneticarray comprising multiple sets of magnets arranged to have Hall-Effectregions that run lengthwise along a sputter target. The system furtherincludes an elongated sputtering electrode material tube surrounding themagnetic array comprising multiple sets of magnets arranged to haveHall-Effect regions that run lengthwise along the sputter target.

During operation, the system carries out a method for nanolaying asurface of a three-dimensional surface by generating and controlling ionflux for direct current high-power impulse magnetron sputtering. Themethod includes providing a vacuum apparatus containing a sputteringmagnetron target electrode; generating a high-power pulsed plasmamagnetron discharge with a high-current negative direct current (DC)pulse to the sputtering magnetron target electrode; and generating aconfigurable sustained positive voltage kick pulse to the magnetrontarget electrode after terminating the negative DC pulse. During thegenerating, program processor configured logic circuitry issues acontrol signal to control at least one kick pulse property of thesustained positive voltage kick pulse taken from the group consistingof: onset delay, duration, amplitude and frequency and modulationthereof.

A method is provided for carrying out a nanolaying of a surface of athree-dimensional surface by generating and controlling ion flux fordirect current high-power impulse magnetron sputtering. The method iscarried out on a system including an RF accelerator and superconductingcavities for depositing high-quality films for providing a nanolayeredcoating on a three-dimensional surface. The system comprises a magneticarray comprising multiple sets of magnets arranged to have Hall-Effectregions that run lengthwise along a sputter target; and an elongatedsputtering electrode material tube surrounding the magnetic arraycomprising multiple sets of magnets arranged to have Hall-Effect regionsthat that run lengthwise along the sputter target.

The method comprises providing a vacuum apparatus containing asputtering magnetron target electrode; generating a high-power pulsedplasma magnetron discharge with a high-current negative direct current(DC) pulse to the sputtering magnetron target electrode; and generatinga configurable sustained positive voltage kick pulse to the magnetrontarget electrode after terminating the negative DC pulse. During thegenerating, program processor configured logic circuitry issues acontrol signal to control a kick pulse property of the sustainedpositive voltage kick pulse taken from the group consisting of: onsetdelay, amplitude and duration.

Additional features and advantages of the invention will be madeapparent from the following detailed description of illustrativeexamples that proceeds with reference to the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

While the appended claims set forth the features of the presentinvention with particularity, the invention, together with its objectsand advantages, may be best understood from the following detaileddescription taken in conjunction with the accompanying drawings ofwhich:

FIG. 1 is a schematic drawing of a system suitable for incorporating thefeatures of the invention;

FIG. 2A depicts a cross-sectional view of a hermetic break sub-assemblyelement of the system schematically depicted in FIG. 1, including an RFantenna, socket interface, and vacuum flange termination;

FIG. 2B depicts an illustrative RF power amplifier, which is, forexample, a compact planar triode structure;

FIG. 2C depicts sub-assemblies from FIGS. 2A and 2B arranged as a poweramplifier assembly for the RF LINAC system schematically depicted inFIG. 1;

FIG. 3 depicts a cross-sectional view of the RF LINAC system includingfour power amplifier assemblies (depicted in FIG. 2C) attached to an RFLINAC cavity and a vacuum chamber containing the RF LINAC cavity;

FIG. 4 schematically depicts an equivalent electrical circuitdiagram/model for the power amplifier assembly, in operation, depicted,by way of example, in FIG. 2C;

FIG. 5A is a photograph of the exterior of an RF LINAC cavity for aradiofrequency quadrupole accelerator;

FIG. 5B is a photograph of interior quadrants of an RF cavity formed byrigid attachment of four vane structures prior to surface modificationand formation of a continuous RF seal;

FIG. 5C is prior art showing major-minor vane construction for an RFQwith alignment shims and RF seals at each interface;

FIG. 6A depicts a cross-sectional view of an illustrative example ofsurface modification, etching and deposition of thin films on a cavity;

FIG. 6B is a photograph of the example illustrated in FIG. 6A inoperation for deposition of high-conductivity copper directly onto amechanical RF seal;

FIG. 6C depicts a composite RF LINAC cavity comprised of one or morebulk substrate materials with one or more material coatings;

FIG. 6C depicts a composite RF LINAC cavity comprised of one or morebulk substrate materials with one or more material coatings;

FIG. 6D depicts an in-situ sputtering electrode emitting ions andneutral particles to coat one or more substrates;

FIG. 6E depicts a close up view of a composite RF LINAC cavity where avane material is rigidly affixed to a vacuum housing withmechanical/thermal interface and the thin-film continuous coating servesas an electrical interface;

FIG. 7A depicts an axial internal view of a sputtering electrodeemitting ions and neutrals to highlight internal coolant flow, magneticassemblies and plasma generation on the exterior;

FIG. 7B depicts a cross sectional view of a sputtering electrode tohighlight the relative rotation of the target material and magneticassemblies;

FIG. 7C is a photograph of a 1.5-meter long sputtering electrodeillustrative example with a magnetic field arranged to create a singleserpentine dense plasma zone around the sputtering electrode;

FIG. 7D is a photograph of an illustrative example of the IMPULSE®+SuperKick™ for cleaning, etching and surface modification;

FIG. 7E is a photograph of an embodiment of the IMPULSE®+Positive Kick™for implantation, intermixing, adhesion, stress control, morphologycontrol, diffusion barriers and capping layers;

FIG. 7F is a photograph of a 6.3-mm diameter sputtering electrodeexample with a magnetic field arranged to create multiple dense plasmazones around the sputtering electrode that can be axially translated;

FIG. 8A depicts an illustration of the IMPULSE®+Positive Kick™ forconformal coating of substrates;

FIG. 8B is a photograph using the in-line cylindrical magnetrontechnology with IMPULSE®, Positive Kick™ and Super Kick™ for conformalthin-film copper coatings to replace conventional electroplating and wetelectrochemistry for stainless steel cryogenic accelerator bellows;

FIG. 9A depicts an illustration of sputter target erosion and wear fornarrow V trenches;

FIG. 9B depicts an illustration of sputter target erosion with relativemovement between the dense plasma regions and sputter target materialfor uniform erosion;

FIG. 10 depicts a comparison between conventional DC sputtering, pulsedDC, traditional HiPIMS and IMPULSE®+Positive Kick™;

FIG. 11 depicts an illustration of the 1^(st) of 3 phases during anIMPULSE pulse operation—the Ultra-Fast HiPIMS phase;

FIG. 12 depicts an illustration of the 2^(nd) of 3 phases during IMPULSEoperation—the Short Kick phase;

FIG. 13 depicts an illustration of the 3^(rd) of 3 phases during IMPULSEoperation—the Long Kick phase;

FIG. 14 depicts an illustration of a continuous process using theIMPULSE®+Positive Kick™+Super Kick™ without breaking vacuum,interruptions or staging;

FIG. 15 is an oscilloscope waveform of a Cu sputtering plasma achieving2 kA peak current in 20 microseconds during the Ultra-Fast HiPIMS phasewith subsequent +200V positive pulse showing Short and Long Kick phases;

FIG. 16 is a photograph of an embodiment highlighting deposition andetching using the Positive Kick™ and Super Kick™;

FIG. 17A is an oscilloscope trace illustrating the ˜10-100 kHz RF-likemodulation of the positive pulse to generate plasma with a positive RFbias;

FIG. 17B is a photograph of the Super Kick™ in etching mode for plasmageneration;

FIG. 18 depicts a schematic representation of the thin-film deposition,etch and surface modification system with IMPULSE® pulse modules andpower supplies;

FIG. 19 is an illustration of the structure zone diagram with twoindependent axes for effective temperature T* and effective sputterparticle energy E* that are addressable with the IMPULSE® and PositiveKick™;

FIG. 20A is a photograph of the IMPULSE® 2-2 system;

FIG. 20B is a photograph of the IMPULSE® 20-20 system;

FIG. 21A is the prior art for electroplating stainless steel cryogenicbellows for RF accelerators;

FIG. 21B is the prior art for a superconducting RF accelerator sectioncomprising multiple spools, bellows and RF cavities needing specificmaterial properties;

FIG. 21C is the prior art showing RF power loss and thermal dissipationdue to poor electrical conductivity with electroplated copper;

FIG. 22A is the prior art showing surface defects, corrosion, trappedmaterial, inclusions and surface asperities in conventional copperelectroplating leading to poor accelerator performance;

FIG. 22B is the prior art showing inclusions in electroplated copper bysize and material impurity;

FIG. 23A is a photograph of a representative multilayermetal-insulator-metal stack deposited on a substrate with a barrierinterface using the IMPULSE®+Positive Kick™ demonstrating surfacesmoothness and ability to control layer properties;

FIG. 23B is a scanning electron micrograph of a diamond-like carbonlayer deposited with the IMPULSE®+Positive Kick™ technique;

FIG. 23C is a scanning electron micrograph of a diamond-like carbonlayer deposited with conventional DC magnetron sputtering highlightingits porosity and voids;

FIG. 24A depicts snapshots of the plasma potential spatial profile forthe representative Long Kick case where a vacuum chamber dominates insurface area over both the substrate and the smaller sputtering target,and the distance between the target and substrate is many mean-freepaths—very little potential drop reaches the substrate for localconformality;

FIG. 24B depicts snapshots of the plasma potential spatial profile forthe representative Long Kick case where the substrate is much larger insurface area than the sputtering target and vacuum chamber componentsare negligible, and the distance between the target and substrate ismany mean free paths—a small potential drop reaches substrate for localconformality;

FIG. 24C depicts snapshots of the plasma potential spatial profile forthe representative Long Kick case where the target is on the same orderas the substrate area, the vacuum chamber components are negligible, andthe distance between the target and substrate is small—nearly all of thepotential drop appears on the substrate for excellent conformality ofplasma bombardment;

FIG. 25A depicts an illustration of the cases represented in FIG. 24A-Cfor potential profiles with their corresponding ion energy distributionfunctions; and

FIG. 25B depicts an illustration of a case where an additional activebias voltage is applied to the substrate for additional ion bombardmentenergy;

FIG. 26 depicts an illustration for a precision fixturing jig to alignand gap RFQ LINAC vanes;

FIG. 27A depicts an illustration of the surface current pathlength,interface losses and multipactoring stress for adjoining RF surfaces andstructures for conventionally processed materials;

FIG. 27B depicts an illustration of a surface current pathlength,interface losses and multipactoring stress for adjoining RF surfaces andstructures processed with the IMPULSE®+Positive Kick™ and Super Kick™techniques;

FIG. 27C depicts an illustration of axial position along a cavity withregions of poor electrical contact due to macroscopic effects;

FIG. 28 depicts an illustration of challenges with vane alignment andgapping;

FIG. 29 is a graphical representation of a low-Q cavity requiring moreinput RF power required to meet cavity stored energy thresholds forparticle acceleration and vane tip electric field variation risk; and

FIG. 30 is a graphical illustration of a high-Q cavity processed with aprecision alignment jig and coating processed with IMPULSE® techniquesfor lower RF power requirements and reduced vane tip variation tosupport higher axial accelerating gradients for overall compactness andpower savings.

DETAILED DESCRIPTION OF THE DRAWINGS

The detailed description of the figures that follows is not to be takenin a limiting sense, but is made merely for the purpose of describingthe principles of the described embodiments.

A structural assembly and system are described that, in operation,inject RF power directly into an accelerator, such as a radio frequencyquadrupole (RFQ) LINAC, while placing both the RF power amplifier itselfas well as the RF input circuitry and the biasing circuitry outside ofthe vacuum environment occupied by the LINAC cavity. A critical aspectof this disclosure is that it allows for the use of the LINAC cavityitself as the output stage of the amplifier, removing any need fortransmission lines between the final amplification stage and the LINACcavity. The described structural assembly arrangement exhibits multipleadvantageous features. The arrangement mitigates the deleterious effectsof multipactoring associated with placing elements associated with theRF power amplifier in a vacuum environment. Moreover, the arrangementenables inspecting/replacing the RF power amplifier without breaking thevacuum seal of the RF LINAC cavity.

A low capacitance hermetic HV break is of particular importance to thefunctionality of the RF power amplifier arrangement described herein.The low capacitance characteristic of the hermetic HV break (describedin detail herein below) ensures a sufficiently low capacitance betweenthe RF power amplifier's output stage and the LINAC cavity. By way of anillustrative example, the hermetic HV break is a piece of aluminaceramic (or other suitable dielectric material) joined, for example bybrazing or other suitable metallic material bonding technique, to copper(or other suitable conductive material) at both ends.

A further aspect of illustrative examples is that both the RF poweramplifier's output stage and the antenna are placed at the same DCpotential as the LINAC system. Additionally, the illustrative examplesprovide a mechanism to directly and easily cool the amplifier andantenna elements via a flowing liquid (e.g. water) cooling loop. Anillustrative example of this aspect of the disclosure would be to routethe cooling loop through the antenna itself, mounted to the anodeelectrode at one end and ground at the other.

By way of an illustrative example, a system is described herein forinjecting RF power directly into an RF LINAC (such as a radio frequencyquadrupole (RFQ) accelerator), while placing both the RF poweramplifier, the RF input circuitry, and the biasing circuitry outside ofthe vacuum environment occupied by the LINAC cavity. An illustrativeexample of such system is schematically depicted in FIG. 1.

Turning to FIG. 1, the primary components of the illustratively depictedsystem include: a vacuum chamber 1 containing a cavity 2 (e.g. one ormore LINAC cavities), one or more of a power amplifier assembly 3(including an RF power amplifier 6, a hermetic break 5, and an antenna4) directly coupled to the cavity 2 structure, an electronic circuitinterface including a set of inputs 7. The set of inputs 7 of theelectronic circuit interface are configured to provide power, biasvoltages/currents, and sufficiently high-power radio frequency energy tothe one or more of the power amplifier assembly 3. The received radiofrequency energy is amplified by the one or more of the power amplifierassembly 3 for transmission into the cavity 2 structure.

By way of further explanation/definition, “directly coupled”, as usedabove to describe the structural relationship between the poweramplifier assembly 3 and the cavity 2, is defined as an electricalenergy coupling relationship such that there is a negligible powertransmission line between the power amplifier assembly 3 outputinterface and the cavity 2 structure. In the illustrative example, suchdirect coupling is achieved by the power amplifier assembly 3 having thehermetic break 5 barrier between the antenna 4 (which couples to thecavity 2 and is held at vacuum) and the RF power amplifier 6 (operatingat atmospheric pressure).

By way of an illustrative example, FIG. 2C depicts a power amplifierassembly that comprises two sub-assemblies. Each of the twosub-assemblies is depicted, by way of further particular example, inFIGS. 2A and 2B. FIG. 2A depicts a sub-assembly including the hermeticbreak 5. Thereafter, FIG. 2B illustratively depicts, by way of example,an example of the RF power amplifier 6 sub-assembly, in the form of acompact planar triode sub-assembly 17.

Turning to FIG. 2A, the sub-assembly including the hermetic break 5 willnow be described by way of a detailed example. By way of illustrativeexample, the hermetic break 5 is generally cylindrical. The hermeticbreak 5 includes a dielectric body 23 that is generally cylindrical inshape and made of, for example, a ceramic material. The hermetic break 5also includes, at opposing ends, the first conductive material 16 a andthe second conductive material 16 b. In the illustrative example, thefirst conductive material 16 a and the second conductive material 16 bare generally ring-shaped and occupy the ends of the generallycylindrically shaped dielectric body 23 of the hermetic break 5. Thesub-assembly illustratively depicted in FIG. 2A also includes a socketinterface 9 to which the output of the RF power amplifier 6 isconnected. Turning briefly to FIG. 2B, a suitable structure, a compactplanar triode (CPT) 17, for connecting the output of the RF poweramplifier 6 to the hermetic break 5 is depicted. With continuedreference to both FIGS. 2A and 2B, the CPT 17 is attached at an anodeelectrode 18 (also referred to as a plate electrode) to the socketinterface 9 of the sub-assembly containing the hermetic break 5structure.

With continued reference to FIG. 2A, the sub-assembly including thehermetic break 5 also includes a fixed potential electrode 8 to whichthe antenna 4 is connected. The fixed potential electrode 8, by way ofexample, is also generally cylindrically shaped. Thus, in theillustrative example, a generally cylindrical space 24 is formed betweenthe fixed potential electrode 8 and the dielectric body 23 of thehermetic break 5. The antenna 4, which occupies an area within anapproximate range of 0.1 in² to 5 in², is also connected to the socketinterface 9 electrode. Due to high currents involved in operation of theillustrative LINAC system, the antenna 4, the socket interface 5, andthe fixed potential electrode 8 are all made from, or at least coatedwith a sufficiently thick layer of, a high-conductivity material, suchas copper. The term “sufficiently thick” here is defined as being equalto or greater than one skin depth at the intended operating frequency ofthe LINAC system. In conjunction with the cavity 2, the above-describedconductive structures determine/establish an effective electricalimpedance (Z1) observed from the output interface of the RF poweramplifier 6.

With continued reference to FIG. 2A, the hermetic break 5 is physicallyconnected, at the first conductive material 16 a and the secondconductive material 16 b to the socket interface 9 (provided in theillustrative example as two physically joined pieces 9 a and 9 b) andthe fixed potential electrode 8 (provided in the illustrative example astwo physically joined pieces 8 a and 8 b). The electrically insulatingceramic material of the dielectric body 23 provides a high-voltage breakpoint between the RF output of the RF power amplifier 6, received viathe socket interface 9, and the fixed potential electrode 8. Thehermetic break 5 also exhibits a characteristic of a sufficiently lowinterelectrode capacitance, which manifests electronically as acapacitive load C1 in parallel with the load Z1 provided by thecombination of the antenna 4 and the cavity 2. The above-describedelectrical circuit characteristics of the hermetic break 5 aresummarized in the effective electrical circuit model of the systemschematically depicted in FIG. 4.

By way of further explanation/definition, a “sufficiently low”interelectrode capacitance is defined such that the inverse of theinterelectrode capacitance is greater than or equal to the angularfrequency of the RF input multiplied by the magnitude of the antennaimpedance. In the illustrative example depicted in FIG. 2A, the hermeticbreak 5 high-voltage break characteristic is carried out by the firstconductive material 16 a and the second conductive material 16 b beingjoined to the dielectric body 23 by two ceramic-to-metal seals (e.g.alumina-to-copper joints achieved via brazing or diffusion bonding),where each one of the two ceramic-to-metal seals is located at an end ofthe generally cylindrical dielectric body 23. The metal sides of eachjoint, which are formed respectively by the first conductive material 16a and the second conductive material 16 b, have a mechanicalstress-relieving structural characteristic/feature 16 to account fordifferences in coefficients of thermal expansion between the twodissimilar materials (metal and ceramic) of the hermetic break 5 andthereby facilitate reliable bonding. A variety of insulator break andhermetic sealing configurations are contemplated for signally couplingthe RF amplifier output with the cavity structure and vacuum chamber. Ina particular illustrative example, directly joining high-conductivitycopper (16 a and 16 b) to the ceramic material (23) yields superior RFpower transmission capability—compared to a traditional Kovar to ceramicbraze process—avoiding a potentially difficult/challenging further stepof subsequently coating exposed metal surfaces in a high-conductivitymaterial, such as copper. While shown as a separate physical feature inFIG. 2A, it is noted that in other illustrative examples the firstconductive material 16 a may be an integral part of the fixed potentialelectrode 8 structure. Likewise, the second conductive material 16 b maybe an integral part of the socket interface 9 structure.

When the antenna 4 configuration is a loop antenna structure, as is thecase in the example illustratively depicted in FIG. 2A, the antenna 4may be constructed from hollow tubing though which coolant may becontrollably passed to achieve desired temperature control of systemcomponents. A coolant input/output structure 13 is depicted in FIG. 2A.The coolant input/output structure 13 is connected to the antenna 4 (ahollow tube structure) via a set of two channels 14 that pass throughthe fixed potential electrode 8, into which the coolant input/outputstructure 13 and the antenna 4 tubes are inserted and then welded,brazed, epoxied or otherwise sealed. Further, a hollow cavity 15 withinthe socket interface 9 for coolant flow allows for more efficientcooling of the RF power amplifier 6.

In accordance with the illustrative example depicted in FIG. 2A, aConFlat (CF) flange 10 may be used in conjunction with a bellows 11 toensure that structural interfaces of the RF power amplifier assembly canbe mated to the vacuum chamber while remaining tolerant to manufacturingerrors in either the power amplifier assembly 3, the cavity 2, or thevacuum chamber 1 that would require the power amplifier assembly 3 tomaintain some variability/adjustability in its positioning.

An alternative to the above approach is to make the vacuum sealpermanent instead of demountable. This could, for example, beaccomplished by replacing the CF flange 10 by a welded, brazed, orepoxied joint. The fixed potential electrode 8 and the bellows 11 areconnected via a cylindrical housing 12, whose function is simply toprovide a structurally sound vacuum barrier between where the poweramplifier assembly 3 mates to the cavity 2 and mates to the vacuumchamber 1.

Regardless of any specific illustrative example, with the RF poweramplifier 6 located on the air-side of the vacuum chamber 1, deleteriouseffects such as multipactoring and surface flashover can be minimized oreven eliminated for the power conditions of a LINAC or other RF cavitystructure. This is a significant improvement over the current state ofthe art. Power dissipation and cooling can further be managed externalto the vacuum environment.

Further, with the illustrative examples, the RF power amplifier 6 of theillustrative RF power amplifier assembly, which may comprise severalinstances of the RF power amplifier 6, can be rapidly changed out forprogrammed maintenance, or at end of life, without venting the vacuumchamber 1. In the illustrative example depicted in FIG. 2C, this is doneby removing the electronic interface through which inputs 7 are applied,and then removing the RF amplifying element 6, which is replaced beforere-inserting the physical interface for the inputs 7. In theillustrative example depicted in FIG. 2C, the socket interface 9includes a threaded socket, into which the threaded anode electrode 18of the CPT 17 is screwed. Furthermore, in the illustrative exampleprovided in FIG. 2B, a grid electrode 19 a cathode electrode 20 and afilament electrode 21 of the CPT 17 are connected to a connectorinterface providing the inputs 7.

Turning to FIG. 3, an illustrative example of the disclosedsystem/apparatus includes the integration of 4 to 12 power amplifiersonto a radiofrequency quadrupole accelerator to produce particle beamsat energies in an approximate range of 2 to 5 MeV. An illustrative crosssection is shown in FIG. 3 showing four power amplifier assemblies 3 a,3 b, 3 c, and 3 d symmetrically arranged around the cavity 2. Suchsystems could be used for the generation of neutrons, gamma-rays andenergetic ions for various scientific, medical or industrial purposes.Integrating the power amplifiers directly onto the radiofrequencyquadrupole accelerator eliminates entire racks of equipment, RF powercombining equipment, waveguides and power conditioning hardware. Sincethe RFQ cavity is a power combining cavity in its own nature, theillustratively depicted/described system/apparatus uses the powercombining cavity for the dual uses of: (1) combining multiple amplifiersfor use on a single LINAC system, and simultaneously (2) setting upelectromagnetic fields for accelerating particles to high energies.

It can thus be seen that a new and useful system for coupling/injectingRF power into RF LINACs has been described. In view of the many possibleembodiments to which the principles of this disclosure may be applied,it should be recognized that the examples described herein with respectto the drawing figures are meant to be illustrative only and should notbe taken as limiting the scope of the disclosure. For example, those ofskill in the art will recognize that the elements of the illustrativeexamples depicted in functional blocks and depicted structures may beimplemented in a wide variety of electronic circuitry and physicalstructures as would be understood by those skilled in the art. Thus, theillustrative examples can be modified in arrangement and detail withoutdeparting from the spirit of the invention. Therefore, the invention asdescribed herein contemplates all such embodiments as may come withinthe scope of the following claims and equivalents thereof.

Traditional structures and systems for fabricating RF LINAC systemsinvolve taking a large billet of special grade material or alloys, suchas niobium metal, beryllium metal, ultra-high purity oxygen-free copper,and precision machining to precise dimensional tolerance for narrowfrequency band resonant cavities for RF acceleration. For manyaccelerator components, only a few percent of the bulk material are usedwith a lot of lost material, time and labor. This is done at great costto preserve material properties; and to minimize the number of lossyinterfaces, tolerance/stack-up errors, hermetic breaks and mismatches.Often a substrate material is used for its superior structuralproperties at a performance cost of electrical or thermal properties.Tradeoff choices include: using stainless steel instead of copper, orthe converse selection of niobium instead of copper. Because electricalproperties dominate in the skin-depth for electromagnetic propagation inmaterials at high-frequencies (e.g. MHz), using a composite structurewith a surface layer that exhibits superior electrical and vacuumproperties.

With a composite structure, different materials may be selected fordifferent components for thermal characteristics, structural support,expansion and contraction, anti-vibration, etc. With the ability to formcomposite structures, novel methods for fabrication, alignment,fixturing, and segmentation facilitates reducing cost and improvingdesign flexibility for weight, size and power reduction and ease ofintegration. In particular, desirable surface material properties (e.g.low electron emission), material purity (e.g. low inclusions, low fieldconcentration), cavity smoothness (e.g. lower field emission, highergradient), near-surface morphology (e.g. limited whisker growth, sparkinitiation), and vacuum tolerance (e.g. low vapor pressure, surfacemobility) can be engineered to improve the characteristics of the RFLINAC.

The manufacturing operations and techniques described herein also allowreplacing bulk, solid niobium materials with thin-layers forsuperconducting cavities using more robust, thermally-conductive andeasier to form/machine/work materials. Because of the diversity ofmaterials that can be deposited onto a range of substrates, thetechnique allows more options and choices for accelerator cavities andcomponents.

The RFQ LINAC is complex to fabricate due to a precision vane structurerequiring vane tip alignment, spacing and assembly into four quadrantsof equal size for RF load balancing. Traditional RFQ LINACs aremanufactured using major-minor vane configurations comprised multipleaxial assemblies integrated together to achieve a desired accelerationlength. Typical RFQ LINACs operated about 200-425 MHz are 10s of metersin length for acceleration to several MeV for hydrogen ions. Thesemachines are large, costly and are typically found at nationallaboratories, medical centers and research universities. Direct sputtercoating on the interior can seal the interfaces between components, suchas vanes, spacers, tuning rods, bellows, etc. However, the sputtercoating methods and structures described herein are broadly applicableto a variety of applications beyond coating the interior surfaces of RFQLINACs.

The thin-film deposition, etching and surface modification method hereinenables composite construction, low-complexity integration andimprovement in surface material properties for higher gradientoperation. FIG. 5A is a photograph of an exterior of an RF LINAC cavityfor a radiofrequency quadrupole accelerator. In the example show, the RFcavity serves as an external vacuum chamber with multiple ports designedfor acceptance of the RF power amplifier assembly depicted in FIG. 1.

FIG. 5B is a photograph of interior quadrants of the example RF cavityformed by the rigid attachment of four vanes structures prior to surfacemodification and formation of a continuous RF seal. Four vane structures5101 are inserted into an RF cavity and bonded into place with amaterial 5102. A precision fixturing jig (not shown) is attached to thefour vane structures 5101 and vane tip alignment, positioning, gapspacing and tolerancing is performed ex-situ, prior to insertion into anRF cavity substrate 5100. Once the properly gapped and aligned vanestructures 5101 are inserted, the fixtured vanes are rigidly attached tothe RF cavity substrate 5100. The attachment structures are varied andinclude, by way of example, soldering, mechanical screws, turnbuckles,epoxy, low-temperature braze, etc. In the example shown in FIG. 5B,conventional solder is used with a low-temperature bake in an inertoven. As detailed in the following sections, the IMPULSE® thin-filmdeposition, etch and surface modification technique is used to coat theinterface with a high-conductivity copper layer for a continuous cavitysurface to achieve high Q. This is in contrast to FIG. 5C that shows aprior art major-minor vane construction for an RFQ with alignment shimsand RF seals at each interface. Because the RFQ LINAC is thermallycycled and materials age, the interfaces between the major and minorvanes need additional compression force with restorative contact tomaintain low resistance for high surface conductivity to RF currents. Asa result, the attainable cavity Q may be 10-80% of the theoreticalmaximum value under ideal operating conditions, e.g. a cavity Q of 4500vs. the 10,000 achievable for smooth, solid surface copper. A widevariety of mixed materials, including for example ceramics,semiconductors and metals, can be deposited on the RF cavity wallsduring a sputtering deposition operation where a majority of RF currentand energy will transport using the known IMPULSE®+Positive Kick™. Byway of illustrative example, the described sputtering depositiontechnique provides good coverage and sealing surfaces forroom-temperature Cu and superconducting cavities, such as Nb or Nb/NbN,Nb₃Sn or MgB₂.

FIGS. 6A & 6B illustratively depict an application of the surfacecoating system and methods of operation disclosure herein. Namely,thin-film etching and deposition on particle accelerator electrodes andelectromagnetic cavity structures are illustratively depicted. FIG. 6Adepicts a cross-sectional area of a four-vane radiofrequency quadrupole(RFQ) accelerator cavity. The internal four quadrants of the RFQaccelerator cavity are subjected to intense electromagnetic fields andsurface RF currents in operation. To achieve high accelerating gradientsduring operation, very high electric fields are used. Therefore thequality of the surface coating in the cavity, including themicrostructure and electrical conductivity, are critically important toachieve high performance. The surface coating structures and methodsdisclosed herein facilitate a surface preparation, cleaning, etching,adhesion and deposition of high-quality materials that improve qualityand performance of the deposited coatings during operation of the RFQaccelerator. In the illustrative example of FIG. 6A, a sputter target(e.g. sputter target 6001) is inserted inside a vacuum environment 6011of an accelerator cavity substrate 6006. Magnetic assemblies (e.g.assembly 6038) inside of the sputter target 6001 generate magneticfields 6012 that generate and sustain dense plasma regions 6013 togenerate ions and neutrals 6004 that well deposit on substrate 6006.This is accomplished, for example, by introducing a gas into the vacuumenvironment 6011 in the range of 0.01-100 mTorr, typically noble gaseslike Ar or reactive gases like N₂, with voltages in the range of200-2000V with magnetic fields on the order of 100-1000s of Gauss.During operation of the sputtering deposition operation, the energeticions and neutral particles 6004 are generated and directed towardssubstrate 6006.

FIG. 6B is a photograph of the illustrative example in FIG. 6A during anactual operation for deposition of high-conductivity copper directlyonto an interior surface of an RFQ accelerator cavity with vanestructures fixtured and soldered directly to the RFQ accelerator cavitysurface. The sputter deposited copper directly coats the interiorsurface including the solder material to make a continuous Cu layerexhibiting excellent sealing and surface properties. In FIG. 6B, thefour (4) sputtering targets 6001 with the dense plasma regions 6013 arecontained in the vacuum environment 6011 with the RFQ cavity substrate6006 visible during insertion. The dense plasma region 6013 is clearlyvisible inside the vacuum environment 6011. High-conductivity copperwith dense nanograin structure can be deposited with an ultra-smoothsurface roughness to withstand high electric field gradients. Thenanograin texture is resistant to slip-plane whisker growth thatpromotes surface electric field concentration and sparking under highelectric field gradients. The illustrative examples described hereinavoid this problem.

Furthermore, the presently disclosed material deposition operation(described in the context of providing a superior sealed copperconducting surface for an RFQ accelerator cavity) can also be used forsuperconducting films and layers, such as Nb, Nb/NbN, etc. Using theIMPULSE® and Positive Kick™ and aspects of this disclosure, the filmmorphology and crystallinity are controlled to achieve preferred grainorientation, grain size, lattice plane matching, surface roughness andother parameters leading to superior residual resistivity ration,current density and magnetic performance.

FIG. 6C depicts a composite RF LINAC cavity comprised of one or morebulk substrate materials with one or more material coatings. Materialsmaking up vanes, such as a vane 6101 are fixtured to a wall of the RFQaccelerator cavity relative to one another according to a particulardesign for the RFQ accelerator and affixed to an RFQ accelerator cavitysubstrate 6100 using a bonding material 6102. The material of the cavitysubstrate 6100 is selected for its desired material properties, such as:structural, thermal, cost and ease of fabrication. The materials thatmake up the vanes, such as the vane 6101 are selected for theirproperties, such as thermal conductivity, coefficient of thermalexpansion, machinability, compatibility for copper coating, etc. Theactual bonding of the vane 6101 to a surface of the cavity substrate6100 is carried out, for example using the bonding material 6102 using,for example, a combination of mechanical and chemical attachmentstructures. The sputtering targets, including the sputtering target 6001with a corresponding magnetic assembly 6038, are inserted into thevacuum environment 6011 for surface modification, etching anddeposition. The sputter target 6001 material can be any of a variety ofmaterials selected to obtain different compositions having differentproperties for particular RFQ accelerator applications.

FIG. 6D depicts a zoomed-in view of the previous figures to provide amore detailed depiction of an in-situ sputtering electrode emitting ionsand neutral particles (neutrals) to coat one or more surfaces of the RFQaccelerator cavity substrate 6100. The energetic ion and neutronparticle flow 6004 is directed at the surface within the RF cavity andaccelerator component to produce a thin or thick film surface coating6103 with engineered properties.

FIG. 6E depicts a further zoomed in close up view of a composite RFLINAC cavity where the vane 6101 is rigidly affixed to a vacuum housingby a mechanical/thermal interface, and the thin-film continuous coatingserves as an electrical interface. The thin/thick film surface coating6103 provides a continuous, smooth electrical path across a transitionfrom the RFQ accelerator cavity substrate 6100 to a bonding material6102 to the material on an outer surface of the vane 6101. At MHz RFfrequencies an electrical skin-depth for electromagnetic propagation isonly a few micrometers. Therefore, from the vantage point of the RFcavity, RF energy cannot reach (“see”) the underlying materials (beyondthe skin-depth) and thus performance can be optimized for amulti-layered composite structure where electric field properties areemphasized within the skin-depth range, and mechanical, structuring,cost, manufacturing properties/considerations predominate at distancesoutside the skin-depth layer.

Conventional wet chemistry and electroplating techniques are limited insubstrate material choices, substrate shape, contamination, surfacematerial finish, and adhesion strength. The presently disclosedinnovative fabrication features described herein are based on use ofconformal physical vapor deposition in combination with surface etching,preparation and modification techniques for a wide range of materials.

FIG. 7A illustratively depicts an axial internal side cross-sectionalview of an end-capped cylindrical magnetron emitting ions and neutralshighlighting internal coolant flow, magnetic assemblies and plasmageneration on the exterior. Sputtering target electrode 7001 is mountedonto an end-capped assembly 7106 with an internal cooling channel 7105flowing coolant over magnetic assemblies 7038 and a sputtering targetmaterial 7001. There may be a target holder between the material 7001and the coolant water and magnetic assemblies 7038. The magneticassemblies are, for example, mounted to a structure that facilitates arotation 7039 of the structures providing dense plasma regions 7013around the sputtering target electrode 7001.

FIG. 7B depicts, in an orthogonal cross sectional view of the structuredepicted in side cross-sectional side view in FIG. 7A, a sputteringelectrode highlighting the relative rotation of the sputtering targetmaterial and magnetic assemblies. The rotation 7039 allows magneticfields 7029 from magnetic assemblies 7038 to move relative to the targetmaterial 7001. In the illustrative example, the magnetic assemblies 7038are mounted to a target holder 7008. A dense plasma zone 7013 generatesenergetic ions and neutral particles 7003 that are directed outward fromthe sputtering target material 7001 towards the surfaces of the RFQaccelerator cavity substrate (not shown) to be coated, etched andmodified.

FIG. 7C is a photograph of a 1.5-meter long sputtering electrodeembodiment with a magnetic field arranged to create a single serpentinedense plasma zone around a sputtering electrode. Electrons orbit thecontinuous serpentine racetrack via Hall Effect ExB forces (aka “themagnetron effect”) from the application of voltage on the sputteringtarget electrode 7001, resulting in generation of an intense plasma zone7013. Because it is a single racetrack, the plasma density is able tobetter load balance over the cylindrical magnetron surface for betteruniformity over the length. In this specific example, a 1.5 m-longplasma region is formed with good uniformity over the length suitablefor azimuthal rotation.

FIG. 7D is a photograph of an end-capped cylindrical magnetron 7106operating with a single serpentine racetrack dense plasma region 7013 onthe sputtering target electrode 7001. In FIG. 7D, the end-cappedcylindrical magnetron 7106 employs the IMPULSE®+Super Kick™ techniquefor generating an electromagnetic field for performing cleaning, etchingand surface modification—as evidenced (when viewed live in operation) bya blue-pink-purple color on the copper sputtering target electrode 7001.In this plasma mode, the end-capped cylindrical magnetron 7106 generateshigh energy Ar+ ions and directs the ions radially outward to clean thesurface of objects (e.g. an RFQ accelerator cavity) to be processed.

Advantageously, during a surface processing and treating operation,within less than a second, IMPULSE® operational parameters can bechanged to switch operation of the assembly from performing acleaning/etching operation to deposition/implantation operations. FIG.7E is a photograph of the same system shown in FIG. 7D employing theIMPULSE®+Positive Kick™ technique for generating an electromagneticfield for performing implantation, intermixing, adhesion, stresscontrol, morphology control, diffusion barriers and capping layers—asevidenced (when viewed live in operation) by a bright green copperplasma color from the sputtering target electrode 7001.

FIG. 7F is a photograph of a 6.3-mm diameter end-capped cylindricalmagnetron 7106 with a different illustrative example with magnetic fieldassemblies 7038 arranged to create multiple dense plasma zones 7013around the sputtering target electrode 7001 that can be axiallytranslated. This configuration is adapted to treat interior surfaces ofstructures having very small diameters and coating the interior of smalltubes and difficult-to-reach locations. However, the structure may alsobe used to treat surfaces of larger items as well.

Using cylindrical magnetron configurations discussed herein above, aswell as others including inverted cylindrical, planar and rotary, theIMPULSE® ultra-fast high-power impulse magnetron sputtering (HiPIMS)technique can be used to generate a dense metal plasma and an ultra-fastvoltage reversal for carrying out Positive Kick™ and Super Kick™techniques to accelerate ions and plasma to the substrate formodification. FIG. 8A depicts an illustration of an example of using theIMPULSE®+Positive Kick™ for conformal coating of substrates. DuringHiPIMS pulses the electrical current can be 10-1000× higher thanconventional DC sputtering. Combined with ultra-fast IMPULSE® pulsingtechnology, peak power densities can be achieved <<100 usec leading tovery high plasma densities. The Positive Kick™ voltage reversal andpositive bias pushes ions and plasma away from the dense magnetic fieldregions on the magnetron to increase the local plasma density near thesubstrate during the pulse. This high-density bulk plasma 831 will havea short Debye length allowing it to penetrate 3D structure 823 of thesubstrate 806. Applying the Positive Kick initially accelerates ionsfrom the magnetic confinement zones with directed energy 868 followingGrad B and eventually float bulk plasma potential up such that aconformal sheath 881 will appear around the substrate 806 and accelerateadditional ions 869 to the substrate. If the features are larger thanseveral Debye lengths, then conformal deposition will result. Anadditional result of the Positive Kick is an increase in ion captureefficiency 864 which is important from an economics perspective.

FIG. 8B is a photograph depicting surface coatings achieved using theend-capped cylindrical magnetron technology with IMPULSE®, PositiveKick™ and Super Kick™ for conformal thin-film copper coatings to replaceconventional electroplating and wet electrochemistry for stainless steelcryogenic accelerator bellows. In the foreground, the substrate to becoated 8006 is made from hydroformed stainless steel suitable forcryogenic applications. The as-received material is inserted into thecylindrical magneton system and IMPULSE® applied with Positive Kick™ foradhesion and surface adatom mobility and Super Kick™ foretching/cleaning. The continuous thin/thick film 8013 is conformal deepinto the bellows channels. The adhesion and film quality are enough tosurvive a 400C air bake and immediate immersion into LN2 withoutspallation, delamination or material failure. The material is cycledthrough >1000 full-range expand-compress strokes without failure of thefilm.

Conformal coatings are achieved on accelerator surfaces, including RFcavities, RF seals, bellows, and actual vane tips, I-H structures,dielectric loading structures, tuning elements and electrodes. Lowsecondary electron emission, smooth and high-field emission limitmaterials can be deposited and well adhered in high stress locations,whereas high-conductivity bulk material can be coated in areas where lowresistance is needed. For the case of the 4-vane RFQ accelerator cavitysurfacing, the vane tips are coated with one type of coating for thehigh field region and the cavity zones are coated with a different typeof film structure. For example, ultra-smooth, nano-crystalline oramorphous high-gradient materials on the vane tips and preferredorientation high-conductivity copper in the cavity zones.

FIG. 9A depicts an illustration of sputter target erosion and wear fornarrow V trenches. Under HiPIMS conditions, the higher magnetic fieldlocation 9044 generates a higher plasma density 9013 leading to morelocal current and sputtering from location 9045 on cosine 9047 relativeto the surface normal. The deeper the V-channel 9043 the less solidangle 9046 for material escape and a higher amount of material recyclingoccurs, lowering the overall deposition efficiency of the system. Formultiple racetracks it is possible to have deeper racetrack grooves onsome than others. This accelerates maintenance cycles. FIG. 9B depictsan illustration of sputter target erosion with relative movement betweenthe dense plasma regions and sputter target material for uniformerosion. With rotation or axial adjustment of magnetic field relative tothe target, improved uniformity and less groove 9047 can be achieved forgreater solid angle emission 9049 and target utilization 9048.

FIG. 10 illustratively depicts a comparison of traditional DC magnetronsputtering (low current, low ionization), pulsed DC (lower current, lowionization but better for reactive gases), traditional HiPIMS (highcurrent, high ionization but low deposition rates), andIMPULSE®+Positive Kick™ (high current, higher ionization rates andhigher deposition rates). Typically, HiPIMS plasma current densities are˜0.3 A/cm2. Using an ultra-fast impulse followed by a Positive Kickpulse can exceed 3 A/cm2 with good film properties and is used as afactor in designing the inverted magnetron structure for high peakpowers for more intense ionization, conformal plasma etching anddeposition.

FIG. 11 depicts an illustration of the 1^(st) of 3 phases during anIMPULSE pulse operation—the Ultra-Fast HiPIMS phase. FIG. 11 is adaptedfrom US Application Publication US20180358213A1 and illustrativelydepicts an ultra-fast high-power impulse magnetron sputtering and thepotential distribution between the sputter target and the substrate.

FIG. 12 depicts an illustration of the 2^(nd) of 3 phases duringIMPULSE® operation—the Short Kick phase. FIG. 12 is adapted fromUS20180358213A1 and illustratively depicts an ultra-fast switching andpositive voltage reversal on the target electrode to a positive voltageand the evolution of the potential distribution across the magneticconfinement region near the target electrode—the Short Kick acceleratingions from the dense HiPIMS plasma region away from the target electrodetypically perpendicular to magnetic field lines.

FIG. 13 depicts an illustration of the 3rd of 3 phases during IMPULSE®operation—the Long Kick phase. FIG. 13 is adapted from US20180358213A1and illustratively depicts a positive potential evolution into the LongKick phase where the plasma potential of the bulk is increased andconformal sheaths form on the substrate and other surfaces where thebulk plasma is commuted.

An aspect of the disclosure provided herein is the ability to control,during operation of the apparatus described herein, the flux and energyof ions deposited/impacted onto substrates for the preparation anddeposition of thin-films with engineered properties. A high level ofcustomization afforded with the combination of ultra-fast high-currentpulsing with rapid positive voltage reversal with the cylindricalmagnetron configuration enables superior and novel films, includingadvanced nanolayer composites and functionally-graded materials withspecific attributes, including high-electrical gradient standoff,high-voltage tolerance, high-electrical conductivity, ultra-smoothsurfaces, oxidation resistance, thermal fracture toughness, crackarresting features, diffusion barriers and anti-wear, anti-corrosion,ductile vs. stiffness, lubricious properties, etc. Specifically, thedeposition of superconductor-insulator-superconductor layers with lowbulk temperature highly sought after by superconducting wire, magnetictape, RF cavity and accelerator engineers.

FIG. 14 illustratively depicts a central advantage in terms of combiningcleaning 14072, etching 14073, ion implantation 14074, adhesion control14075, stress management 14076, bulk material deposition 14077,diffusion barriers or insulating layers 14078, and reactive/cappinglayer 14079 depositions. With precision ion energy control, theultra-fast IMPULSE® with positive voltage reversal can remove surfacecontaminants, etch near-surface damage, develop a mixing interface for agood adhesion layer, to support stress-controlled layer(s)s that enablesbulk films to be grown with suitable interface and capping layer(s).FIG. 14 depicts an illustration of a continuous process 14071 using theIMPULSE®+Positive Kick™+Super Kick™ without breaking vacuum,interruptions or staging.

FIG. 15 is an oscilloscope waveform of a Cu sputtering plasma achieving2 kA peak current in 20 microseconds during the Ultra-Fast HiPIMS phasewith subsequent +200V positive pulse showing Short and Long Kick phases.The voltage waveform 15055 and a current waveform 15058 for a −750V, 2kA peak current HiPIMS pulse achieving a plasma current density of 5A/cm2 on the cylindrical magnetron with a copper sputtering target witha positive kick pulse of +200V, 125 A peak current highlighting a shortkick 15056 and a long kick 15057. The IMPULSE® technology describedherein drives plasma generation at high dI/dt to achieve rapidionization for subsequent voltage reversal and Positive Kick™ toaccelerate ions and plasma into substrates for superior cleaning,etching, preferred-orientation deposition and deposition with stress andmorphology control. The technology also allows for synchronization withpulsed DC bias supplies for time windowed acceleration into thesubstrate for additional control as taught in US20180358213A1.

Depending on local factors such as pre-ionization, target material,magnetic field, pressure, geometric curvature, sputtering gas, surfacechemistry, adsorbed gases, etc, the main negative pulses on the voltagewaveform 15055 are typically in the range of −400V to −1200V. Using theultra-fast switching topology typical high-current pulse widths are lessthan 100 usec, with a typical range of 20-50 usec. The Positive Kick™amplitude on the voltage waveform 15055 are typically in the range of+0-600V. For users who do not want the short kick ion population groupto be accelerated away from the sputter target, shown in the currentwaveform for the short kick 15056, the onset delay in the positive kickwould be set to after this time period typically set at 20-40 usec. Theionization rate and plasma density near the sputtering target is highlycoupled with the effective current density. Effective current densitiesare in the range of 0.1-10 A/cm2.

FIG. 16 is a photograph of a conventional planar magnetron operatingwith ultra-fast short main pulse for deposition and subsequent RF-likemodulation of the Positive Kick™ pulse to generate and sustain asecondary plasma with positive potential relative to the substrate foretching. Each pulse cycle would be a combination of deposition andetching—in the case with a copper sputtering target to achieve preferredorientation copper deposition such as Cu(211) vs. Cu(111) vs. Cu(100).The etching parameters are adjusted for preferred orientation andepitaxial growth conditions. A sputter target 16001 is processing both anegative main pulse and an RF-modulated positive pulse. The dense plasmaregion 16013 over the racetrack is brilliant white-green from the Cu Iand Cu II optical emission lines. A central plasma region 16080 excitedby the RF-modulation of the positive voltage is colored pink from Ar Iand Ar II excitation. The central plasma region 16080 extends all theway down to an insulating substrates 16082 exhibiting combination fordeposition and etching a surface 16083. A conformal plasma sheath 16081extends down to the insulated substrates 16082. Using the combinationfor deposition and etching preferred orientation films can be deposited.

FIG. 17A is an oscilloscope trace illustrating the ˜10-100 kHz RF-likemodulation (such as frequency and/or amplitude) of the positive pulse togenerate plasma with a positive RF bias. FIGS. 17A and 17B arephotographs highlighting the Super Kick™ mode for extended plasmageneration away from the magnetic field and etching on substrates with asample oscilloscope waveform 17086 (FIG. 17A) showing 77 kHz operation,current waveforms 17058 for the RF-like oscillation and voltagewaveforms of an RF-like voltage application 17085. The photograph inFIG. 17B shows a bare target electrode 17001 without the bright visibleemission from the racetrack region. The absence of any dense plasmaregion shows there is no sputtering of the target occurring. A brightcentral plasma region 17080 follows the magnetic nozzle/cusp expansioninto the target electrode and is a commuted to a target electrode 17001at elevated positive potential. The resulting etching plasma extendsdown to a substrate 17084 with a visible plasma sheath 17081 conformingon the samples. The Super Kick™ mode can be indefinitely sustained undera range of operational conditions for direct etching. The Super Kick™can also be used in conjunction with a negative DC bias on the substratefor additional flexibility in materials processing.

FIG. 18 depicts a schematic representation of the thin-film deposition,etch and surface modification system with IMPULSE® pulse modules andpower supplies. FIG. 18 is a schematic a block diagram showing anillustrative example of an electrical component/circuitry arrangementbetween a sputter target electrode, a return electrode, a substrate, aplasma in a vacuum environment and one or more IMPULSE® HiPIMS pulsemodule(s) (its main and kick supplies) and any IMPULSE® bias pulsemodule supplies. The schematic block diagram in FIG. 18 outlines ageneric setup of IMPULSE® systems for deposition and etching. Highvoltage electrical pulses are provided from the external pulsed powermodules directly to the sputter target through appropriate insulationand low-impedance connections. By rotating the magnetic assemblies, thisallows for low-impedance electrical connections to the sputter targetholder for efficient power transfer and coupling. The IMPULSE® modulesare designed for parallel synchronous and asynchronous operation.Therefore, multiple units can pulse in parallel to delivery neededpower, risetime and plasma density for a sputtering target electrodeconfiguration.

FIG. 19 illustratively depicts an example structure zone diagram withtwo independent axes for effective temperature (T*) and effectivesputter particle energy (E*) that are addressable with the IMPULSE® andPositive Kick™. FIG. 19 expands on the control of thin-filmmicrostructure and morphology via illustration of the Andre Anders'modified Thornton Structure Zone Diagram for generalized energeticcondensation. Adjustment of the HiPIMS pulse amplitude, pulse width,timing, peak current density, repetition rate and pressure for a givensubstrate-to-sputter target distance, magnetic field geometry and fielddistribution, allows control over the main pulse particle flux (T*)which is approximate as a thermal spike. More intense short pulses withhigher particle loading over shorter periods has a high temperatureeffect allowing the deposited material to equilibrate and adjust towardsfibrous transitional grains (zone T), columnar grains (zone 2) andrecrystallized grain structure (zone 3). Adjustment of the positive kickpulse amplitude, short/long kick pulse, onset delay and any super kickeffect for RF-like oscillations for a given magnetic field, cuspmagnetic null geometry, pressure and available plasma resulting from themain IMPULSE® HiPIMS pulse will allow adjustment of the effective energy(E*) and adjustment of the thin-film microstructure and morphology.Essentially controlling the IMPULSE® and the positive kick allowsmovement all over the Anders/Thornton SZD, even achieving fine-grainednanocrystalline films with preferred orientation and region oflow-temperature low-energy ion-assisted epitaxial growth and dense,amorphous glassy films. The process engineer can move around the SZD toachieve tensile/compressive stress control, columnar growth vs.nanocrystalline with preferred orientation, etc.

FIG. 20A and FIG. 20B are photographs of an IMPULSE® 2-2 system and anIMPULSE® 20-20 system used as a power supply in the systems describedherein in implementations of the present disclosure.

FIG. 21A is an example of a bellows structure having a surfacetreated/formed using a prior art approach for electroplatingstainless-steel cryogenic bellows for RF accelerators. In the imageprovided in FIG. 21A, the variable quality of the copper plating may beobserved with an inability to deposit plate material on the sidewalls ofthe vacuum bellows section due to masking and nickel strike layerdifficulties. Prior art method may be replaced, with beneficial resultsof better surface treating/plating by use of the deposition/sputteringoperations of the present disclosure.

FIG. 21B illustratively depicts a prior art arrangement for asuperconducting RF accelerator section comprising multiple spools,bellows and RF cavities needing specific material properties. Thepresent disclosure addresses multiple sections with wide application.

FIG. 21C illustratively depicts performance properties of a prior artshowing RF power loss and thermal dissipation due to poor electricalconductivity with electroplated copper. The thickness of the filmdetermines both magnitude of RF losses and ability of the structure toconduct that deposited thermal energy outward. This is important for notonly accelerator cavities but also bellows sections, transfer tubes andother beam structures.

Trapped RF modes are a source of heating that exist in acceleratorstructures such as bellows. For superconducting accelerator cryomodulesthat are kept at liquid He temperatures, any thermal energy depositedhere will be removed solely via conduction along the bellows surface toits edges. To minimize heating, as close to pure (e.g. high RRR) copperfilms having a thickness of >10 μm is highly desirable for theseapplications. Starfire's IMPULSE®+Positive Kick™ technology addressesthis by enabling stress control in the deposited films. This allows theprocess engineer to deposit films having little to no internal stress,which is critical for thick, large-area films.

The present disclosure allows very thick, stress-controlled,fully-dense, high-conductivity, well adhered coatings to address thischallenge, as shown in FIG. 8B. Low-temperature deposition using thePositive Kick and IMPUSLE allows a higher effective T* and E* to get theright orientation without high bulk temperature that results ininterdiffusion of the layers. Added knob of kick voltage/duration ismeaningful. Changes T* on the Thornton zone diagram without requiringdirect heating of the substrate. Low actual substrate temp preventsdiffusion in nanolayered materials (e.g. SIS structures). Adjustablesurface mobility good for low defects are critical for SC films.

FIG. 22A is a photograph collection for a surface treated according tothe prior art showing surface defects, corrosion, trapped material,inclusions and surface asperities in conventional copper electroplatingleading to poor accelerator performance. The IMPULSE®+Positive Kick™ andSuper Kick™ modes controls net deposition, etching, or doing both forsmoothing/roughness-fill. Releveling a surface is beneficial tohigh-gradient (i.e. spark-resistant or spark-tolerant) acceleratorfilms. The initial spark resistance is in smoothness, but that theoverall tolerance comes more from a lack of inclusions that are providedby depositing a controlled film in an atom-by-atom process vs. bulkcasting and machining. After a first arc, the local surface is no longersmooth. Therefore, the film impurities/defects/inclusions determineperformance of a treated surface.

FIG. 22B is an illustrative summary of performance of surfaces treatedaccording to the prior art. The summary shows the presence of inclusionsin electroplated copper by size and material impurity. The surfacetreatment and formation operations and structures described hereinaccording to the present disclosure enable controlled deposition ofmaterials on an atom-by-atom basis, greatly limiting inclusion size andcomposition to suppress local field enhancements and multipactoring andsparking.

The proposed illustrative examples using conformal ionized physicalvapor deposition replaces wet chemical electroplating (e.g. Cu) forstainless-steel bellows and specialty vacuum components used onaccelerator structures. Wet chemical electroplating is beingprogressively phased out due to its damaging environmental impact,hazardous chemical handling, high cost, and lack of experiencedtradespeople in the field. In the EU there are proposals and timelinesfor the complete phase out of all electroplating in the coming years,making investment in alternative technologies important. There are knownissues with surface finish/roughness (including macroscopically visiblestriations in the plating), inclusions, particulates from both thecopper plating itself, as well as those potentially introduced duringthe electroplating or subsequent surface smoothing steps (e.g. Mo-woolpolishing or bead blasting).

FIG. 23A is a photograph of a representative multilayermetal-insulator-metal stack deposited on a substrate with a barrierinterface using the IMPULSE®+Positive Kick™ demonstrating surfacesmoothness and ability to control layer properties. FIG. 23B is ascanning electron micrograph of a diamond-like carbon layer depositedwith the IMPULSE®+Positive Kick™ technique. FIG. 23C is a scanningelectron micrograph of a diamond-like carbon layer deposited withconventional DC magnetron sputtering highlighting its porosity andvoids. The microstructure and morphology of the thin-film coatings canbe controlled using the IMPULSE®+Positive Kick™ as described in U.S.application Ser. No. 16/801,002, filed Feb. 25, 2020, and entitled“METHOD AND APPARATUS FOR METAL AND CERAMIC NANOLAYERING FOR ACCIDENTTOLERANT NUCLEAR FUEL, PARTICLE ACCELERATORS & AEROSPACE LEADING EDGES.”Production of nanocrystalline or preferred orientation films near thesurface can minimize surface asperities, whisker growth and slip-planeprotraction growth kinetics that are partially responsible forelectric-field concentration, multiplication and the formation ofsparks/arcs.

On important aspect for the application of the Positive Kick™ forconformal depositions is the Long Kick and ability to bring dense plasmaand local sheath potential drop around the substrate to be coated, asshown in FIG. 8A. If the target plasma area is small compared to thevacuum chamber and the chamber is located proximal to the sputtertarget, then a large fraction of the Positive Kick™ energy flow will beto the chamber vs. the substrate. FIG. 24A depicts a theoreticalsnapshot of a plasma potential spatial profile for the representativeLong Kick case where a vacuum chamber dominates in surface area overboth the substrate and the smaller sputtering target, and the distancebetween the target and substrate is many mean-free paths—very littlepotential drop reaches the substrate for local conformality.

FIG. 24B depicts a corresponding snapshot of the plasma potentialspatial profile for the representative Long Kick case where thesubstrate is much larger in surface area than the sputtering target andvacuum chamber components are negligible, and the distance between thetarget and substrate is many mean free paths—a small potential dropreaches substrate for local conformality. A better condition isillustratively depicted in FIG. 24C that shows a plasma potentialspatial profile for the representative Long Kick case where thesputtering target is on the same order as the substrate area to betreated/coated with a material from the sputtering target, the vacuumchamber components are negligible, and a distance between the target andsubstrate is small—nearly all of the potential drop appears on thesubstrate for excellent conformality of plasma bombardment.

FIG. 25A illustratively depicts cases represented in FIG. 24A-C forpotential profiles with their corresponding ion energy distributionfunctions for the Long Kick. Not shown are the ion contributions for theShort Kick and acceleration away from the dense magnetic region. Theseillustrations highlight the normal, abnormal and obstructed glowdischarge regimes encountered during the Long Kick phases. FIG. 25Bdepicts an illustration of a case where an additional active biasvoltage is applied to the substrate for additional ion bombardmentenergy.

Because of the high-quality thin and thick films that can be conformallydeposited on composite material surfaces from the IMPULSE® techniques,it is possible to separate an often difficult and physically challengingprocess of RFQ vane tip alignment from fabricating the sealed RFQ cavitystructure. As shown in the illustrative prior art depicted in FIG. 5C,the conventional approach to assembling the RF LINAC structures is tofabricate whole 3D section cavities, such as the major-minor vaneconstruction, for assembly. Very precise and complicated constructionprocedures and machinery are often required, such as a 5 or 6 axis CNCmilling machine. Vane sections can be bonded to the RF cavity andthereafter conformally coated in accordance with the present disclosure.This staged approach to fabricating RF LINACs permits less expensivefabrication techniques and smaller sized components to be used.

FIG. 26 illustratively depicts an example of a precision fixturing jigthat facilitates aligning and gapping RFQ LINAC vanes. The particle beamchannel 26113 is defined by a relative placement of the accelerator vanetips such as a vane tip 26112 that are placed around the center point inthe cross-section view provided in FIG. 26. Each of the four vanes,including, for example a vane 26101 are aligned and gapped by aprecision jig 26110 and affixed with ones of mechanical supports such asa mechanical support 26111. Vertical, horizontal, angular, vaneundulation, intra-vane capacitance, vane tip spacing, and otherproperties can be measured and controlled, by removable fasteners orother mechanical means such as pins, turnbuckles, shims and spacers,with access to the vanes without the rest of the RF cavity structureintroducing additional degrees of freedom and sources of error. Theprecision alignment jig 26110 additionally includes, for example,measurement slots and ports for conducting diagnostics and insertingprobes (e.g., optical, vibrational, acoustic, electro-magnetic,capacitive bead, hairpin probes, etc). The precision alignment jig 26110can be fabricated of materials that differ from the underlying vane26101 materials. Depending on the bonding method and the processingconditions used to join vanes 26101 with the rest of the RF cavity body26100, the precision alignment jig 26110 material may be selected forCTE properties, stiffness, etc. to maintain alignment and gap spacing ofthe vane tips 26112 during the bonding to the RF cavity 26100.

Performance of an RF accelerator greatly depends on electricalproperties of the RF accelerator cavity. The electrical properties areinfluenced by skin-depth effects, surface roughness, grain size andboundaries, microfissures, electron transport and scattering effects offdefects and inclusion, local permittivity, permeability and fielddiffusion, etc. These properties can be modified by theIMPULSE®+Positive Kick™ and Super Kick™ techniques to improve theintrinsic electrical properties. Extrinsic properties are influenced bychanges cavity shape and vane tip position and alignment, affectingfrequency, eigenmodes, dipole or higher-order modes, etc. Combined withmacroscopic shape, variations is shape, interferences, frequency,temperature, expansion effects, and thermal dissipation characteristics,surface roughness, and the ability to maintain and its electricalproperties. FIG. 27A, described next, illustratively depicts anillustration of the interface losses for adjoining RF surfaces andstructures.

FIG. 27A depicts a cross-section view of an electrical component toillustratively depict surface current pathlength, interface losses andmultipactoring stress for adjoining RF surfaces and structures forconventionally processed materials that result in relatively unevenouter conductive surfaces. Conventional room-temperature RF LINACs useelectropolished copper coatings or are machined out of a solid block ofcopper to obtain required/desired surface material properties. Wetchemistry techniques for electropolishing and leveling vary based onconformal anode material construction, water flow, temperatures,orientation of etching/plating system, processing length, solutionbuffering and complex polarity kinetics with high-current bath powersupplies. Even with these techniques, conventional wet chemistrytypically achieves surface roughness values exceeding the skin-depth forhigher frequency microwave drivers, e.g. >500 MHz. As a result, theskin-depth current flow 26130 travels very close to the surface. Becausethe skin-depth current flow 26130 is carried near the surface within afew skin depths, the effective current pathlength is significantly morethan the perimeter of the RF cavity. This additional pathlengthincreases the effective resistance of the RF cavity placing an upperlimit on cavity Q. Interfaces between different assemblies and materialsbecome more problematic for localized electric field and potentialdifferences.

In the FIG. 27A example, an undercut (gap) between tan RF cavitysidewall 26100 and a vane 26101 adds additional pathlength (the distanceadded by the path entering into and exiting the undercut (gap).Moreover, a potential difference will appear across the junction leadingto multipactoring electron emission site risk.

FIG. 27B illustratively depicts the surface current pathlength,interface losses and multipactoring stress for adjoining RF surfaces andstructures arising from RF accelerator cavity surface treatments usingthe IMPULSE®+Positive Kick™ and Super Kick™ techniques. The surfacecleaning and etching process provide leveling effect for hills and allowfor resputter to fill the valleys. The deposition processes allow forimplantation/intermixing for boundary adhesion and strength for theresulting continuous conducting surface 26103 that can be deposited, bysputtering/deposition using the sealing surface material depositionprocedures described herein, to the desired thickness by control of thefilm stress, nanostructure and orientation. By adjusting the PositiveKick™ values for optimal adatom mobility, ultrasmooth surfaces can bedeposited with the IMPULSE® with average roughness less than the skindepth. The resulting ultra-smooth surface pathlength approaches an idealgeometrical case for lower effective resistance. Furthermore, themicrofissures and surface interfaces are coated and covered with thecontinuous film 26103, thus minimizing multipactoring site risk. Thecontinuous film 26103 is selected from a variety of source/sputtertarget materials according to the desired conductivity of the resultingcavity surface, including superconducting materials. The resultingcontinuous film 26103 increases the cavity Q to support higheraccelerating gradients and/or reduce power consumption.

FIG. 27C illustratively depicts an axial position along a cavity withregions of poor electrical contact due to macroscopic effects such asbending stress, thermal expansion, material mismatch and poor mechanicalRF seals at interfaces. For RF LINACs constructed with sections orsegments, mechanical fasteners 26114 are used to attach and compress theinterfaces. Often RF compression seals are used to make hardmetal-to-metal contact, to thereby minimize electrical impedance.Unfortunately, macroscopic discontinuities 26115 form that lead touneven current flow in the RF cavity, lower Q performance andvariability over operation of the accelerator for operating parameters.Desirably, the interface between the RF cavity 26100 and the vane 26101are continuously fixtured along the entire length of the acceleratorcavity structure. This is typically accomplished using high-temperaturebrazing. Unfortunately, the braze material conductivity is lower thanthe conductivity of bulk alloys. Moreover, the thermal cycling of the RFLINAC has a major impact on dimensional tolerances and stability.However, the added engineering cost and development is eliminated usingthe IMPULSE® technique for the resulting continuous coating.

RF LINAC performance is further compromised by cross-sectionalmisalignment/positioning of vanes and resulting gaping between ends ofthe vanes, as shown in the illustrative cross-section in FIG. 28.Particle acceleration occurs due to the particle experiencing aquasi-continuous acceleration down the length of a channel formed by aset of vanes at a central location of the RF accelerator cavity. Thealternating vane undulations continually change as the particle velocityincreases.

FIG. 28 highlights common vane mis-alignments for the critical vane tipregion that lead to lost beam transmission and very high electric fieldin the gap, which leads to vane tip sparking. Vanes 26101 are positionedrelative to a beam axis located at the origin of the x-y lines. Basicmisalignments include inline shifts along the x-axis 26122, the y-axis26121 and z axis (not shown). With misalignment introduced (as shown inFIG. 28) the vane tips are no longer equidistant, which affectsintra-vane capacitance arising from gaps, such as a gap 26120, in eachquadrant. The changed capacitance affects shunt impedance,electromagnetic power balance and lowers the efficiency of powerinjection into the accelerator. Overcoming the signal degradation byincreasing input RF power increases a local electric field 26125 at vanetips, thereby increasing the probability of sparking above a criticalfield threshold. Misalignment and deformation due to heating canintroduce twisting on vanes such as the twisting misalignment on a vane26123, resulting in changing a surface normal of the vane tips andintroducing additional fringing to the local electric field 26125,resulting in an asymmetric focusing field for the quadrupole modeguiding the particles off axis 26124. The net result from these effectsare, detuned RF cavity properties, lower cavity Q, increased sparkingrisk and lost beam transmission. Some of the undesirable effects arisingfrom misalignment of vanes can be compensated with increased RF power,higher vane tip voltages, longer LINAC cavity length for lower overallgradient, etc. However, the precision alignment jig discussed earlierprovides the means to mitigate vane misalignment and the IMPULSE®technique allows for continuous coatings for reduced power consumptionand/or reduction in LINAC size, weight and power, i.e. the Centurion®RFQ LINAC system.

FIG. 29 graphically represents a low-Q cavity requiring high levels ofinput RF power to meet cavity stored energy thresholds for particleacceleration and vane tip electric field variation risk. In thisrepresentation, the cavity stored energy threshold 26117 is a functionof the LINAC parameters, such as frequency, accelerating gradient,accelerator length, vane tip spacing and beam envelope, and theeffective conductivity of the cavity, shunt impedance and the resultingQ factor. This equates to a nominal vane-tip electric field threshold26117 for a perfectly aligned system. Variations in the vane alignmentwill provide a deviation from the optimal case for each position alongthe cavity, as well as sub optimal surface conductivity, increasedpathlength, higher-order modes and de-tuning of the cavity resonance.The resulting vane-tip electric field profile 26116 is upshifted to anelevated vane-tip electric field profile 26119 to achieve the thresholdvalue required for acceleration down the length of the accelerator. Thepenalty is the increase in RF power 26118 to achieve a desired magnitudeof particle acceleration. This comes at a cost since the peak vane-tipelectric field 26119 limits the sparking condition and overall risk.

FIG. 30 graphically illustrates a high-Q cavity achieved by fabricationusing the manufacturing and surface processing techniques describedherein, including using a precision alignment jig and forming a coatingthat is processed according to IMPULSE® techniques. The resultingimproved vane alignment precision and surface quality facilitatesproduction of an RFQ accelerator that achieves lower RF powerrequirements and reduced vane tip variation to support higher axialaccelerating gradients for overall compactness and power savings. Withthe increase in conductivity and reduction in resistive losses, thehigher cavity Q maintains the required cavity stored energy at a lowerinput RF power threshold 26117 compared to the representation in FIG. 29by an amount 26126. The peak vane-tip electric field 26119 is greatlydecreased by an amount 26128 close to the cavity threshold level 26117with a well-regulated vane tip electric field profile 26129. Thereduction in E-field variation on the vane tips as shown in the profile26129 allows greater safety margin and relaxes the Kilpatrick Limit forRF breakdown allowing higher accelerating gradients, wider frequency ofoperation and beam configurations, such as achieving >4 MV/maccelerating gradients for reduced power, size, weight and cost.

In general, the realm of achievable accelerating gradients is limited byarcing/sparking within the cavity itself. This is typically thedominating factor that determines the maximum electric field strengthsthat are sustainable within the cavity. As an example, the Kilpatrickcriterion for breakdown-free operation, which is given by

${f = {\left( {{1.6}4\mspace{14mu} {MHz}} \right)\left( \frac{E}{1\mspace{14mu} {MV}\text{/}m} \right)^{2}\exp \; \left( {{- {8.5}}\left( \frac{1\mspace{14mu} {MV}\text{/}m}{E} \right)} \right)}},$

states that the maximum electric field (again, for breakdown-freeoperation) in a 600 MHz copper cavity structure is approximately 23MV/m. This is effectively a soft limit placed on the maximum electricfield at the vane tips of the RFQ structure, with so called ‘braveryfactors’ (a multiple of the Kilpatrick criterion) of 1-2 being typical.As the electric field is raised beyond this value, arcing may becomeincreasingly frequent. Since it is the electric field that isresponsible for acceleration, this effectively places a limit on theachievable accelerating gradient that sets an upper bound on thevane-tip electric field in FIG. 30.

However, since arcing/sparking occurs almost exclusively at the vanetips in an RFQ structure, where the currents are virtually zero, theability to either 1) coat the vane tips in an arc/spark-resistantmaterial as a finishing step, such as Be or TiN, or 2) have thearc/spark-resistant material already present (whether as a film coatingor as the bulk vane material itself) and then selectively apply thehigh-conductivity coating everywhere but the vane-tips will allow for anoverall structure that is both high-Q and arc/spark-resistant. Simplyput, the ability to utilize different materials for the cavity walls(where the currents are high) and the vane tips (where electric fieldsare high and arcing is a problem) allows the arcing limitations to beeffectively decoupled from the material limitations of the highconductivity (Cu) cavity coating. The IMPULSE® techniques improve thesmoothness of the vane tip surface to minimize local electric fieldconcentrations. However, the material purity of the coating, workfunction and field-enhancement/secondary electron emission properties,coating morphology and nanostructure to minimize/inhibit whisker growthand surface atom mobility, and elimination of inclusions and local fieldconcentrators, such as particles and impurities found in traditional wetchemistry, are also important variables controlled by the IMPULSE® andthe deposition techniques in this disclosure.

All references, including publications, patent applications, andpatents, cited herein are hereby incorporated by reference to the sameextent as if each reference were individually and specifically indicatedto be incorporated by reference and were set forth in its entiretyherein.

The use of the terms “a” and “an” and “the” and similar referents in thecontext of describing the invention (especially in the context of thefollowing claims) are to be construed to cover both the singular and theplural, unless otherwise indicated herein or clearly contradicted bycontext. The terms “comprising,” “having,” “including,” and “containing”are to be construed as open-ended terms (i.e., meaning “including, butnot limited to,”) unless otherwise noted. Recitation of ranges of valuesherein are merely intended to serve as a shorthand method of referringindividually to each separate value falling within the range, unlessotherwise indicated herein, and each separate value is incorporated intothe specification as if it were individually recited herein. All methodsdescribed herein can be performed in any suitable order unless otherwiseindicated herein or otherwise clearly contradicted by context. The useof any and all examples, or exemplary language (e.g., “such as”)provided herein, is intended merely to better illuminate the inventionand does not pose a limitation on the scope of the invention unlessotherwise claimed. No language in the specification should be construedas indicating any non-claimed element as essential to the practice ofthe invention.

Exemplary embodiments are described herein known to the inventors forcarrying out the invention. Variations of these embodiments may becomeapparent to those of ordinary skill in the art upon reading theforegoing description. The inventors expect skilled artisans to employsuch variations as appropriate, and the inventors intend for theinvention to be practiced otherwise than as specifically describedherein. Accordingly, this invention includes all modifications andequivalents of the subject matter recited in the claims appended heretoas permitted by applicable law. Moreover, any combination of theabove-described elements in all possible variations thereof isencompassed by the invention unless otherwise indicated herein orotherwise clearly contradicted by context.

What is claimed is:
 1. A system for depositing high-quality films forproviding a nanolayered coating on a three-dimensional surface of an RFaccelerator cavity and associated superconducting cavities, the systemcomprising: a magnetic array comprising multiple sets of magnetsarranged to have Hall-Effect regions that run lengthwise along a sputtertarget; and an elongated sputtering electrode material tube surroundingthe magnetic array comprising multiple sets of magnets arranged to haveHall-Effect regions that run lengthwise along the sputter target,wherein, during operation, the system is configured to carry out amethod for nanolaying a surface of a three-dimensional surface bygenerating and controlling ion flux for direct current high-powerimpulse magnetron sputtering, the method comprising: providing a vacuumapparatus containing a sputtering magnetron target electrode; generatinga high-power pulsed plasma magnetron discharge with a high-currentnegative direct current (DC) pulse to the sputtering magnetron targetelectrode; and generating a configurable sustained positive voltage kickpulse to the magnetron target electrode after terminating the negativeDC pulse, wherein during the generating, program processor configuredlogic circuitry issues a control signal to control at least one kickpulse property of the sustained positive voltage kick pulse taken fromthe group consisting of: onset delay, duration, amplitude and frequencyincluding modulation thereof.
 2. The system of claim 1 wherein thegenerating a configurable sustained positive voltage kick pulse iscarried out using a capacitive stored power source and a positive pulsepower transistor, and wherein the control signal is issued, during thegenerating, to the positive pulse power transistor.
 3. The system ofclaim 1, further configured to provide a coating on a radio frequency(RF) accelerator having an RF accelerator cavity comprising acylindrical surface disrupted by multiple vanes, each one of themultiple vanes having respective bases adjoining the inner cylindricalsurface.
 4. The system of claim 3, further comprising an alignment jig,the alignment jig being configured to position ones of the multiplevanes relative to at least another one of the multiple vanes duringfabrication of the RF accelerator to facilitate aligning each of themultiple vanes within the RF accelerator cavity during fabrication ofthe RF accelerator.
 5. The system of claim 1 wherein, during operation,the sputter target rotates relative to magnets of the magnetic array tofacilitate a sputter target material utilization of greater than 50%. 6.The system of claim 1 wherein, during operation, the surface to becoated is processed by cleaning, etching, intermixing, adhesion, stresscontrol, bulk film growth, diffusion layers and/or capping layers in acontinuous process.
 7. The system of claim 3, wherein after performing asputter coating operation on the RF accelerator cavity, the RFaccelerator exhibits properties of: sputter material-sealed surfaces andinterfaces of the RF accelerator cavity, improved conductivity, reducedeffective current pathlength, wherein the properties, in combination,result in a relatively improved Q value in relation to the RFaccelerator without the sputter coating operation.
 8. The system ofclaim 3, wherein the sputter coating operation is performed on amultiple component assembly of the RF accelerator including assembledcomponents comprising: the multiple vanes, a cylindrical cavity body,and vacuum envelope.
 9. The system of claim 8, wherein the sputtercoating operation is performed after a vane attachment process whereones of the multiple vanes are mechanically attached to a surface of theRF accelerator cavity, wherein the sputter coating operation provides acoating of the sputter target material over joints and interfaces atattachment points between the multiple vanes and the surface of the RFaccelerator cavity to render a continuous, high conductivity surfaceproviding a lower resistance and a higher Q in relation to an RFaccelerator cavity that does not undergo the sputter coating operationwhere the coating of the sputter target material over joints andinterfaces is provided.
 10. The system of claim 9 wherein the mechanicalattaching of the vanes is performed at a low-temperature, therebyfacilitating keeping within dimensional tolerances and reducing degreeof distortion of ones of the multiple vanes arising from cool down. 11.The system of claim 7 wherein the deposited film structure is comprisedof grain structure with preferred orientation along the RF acceleratorcavity current flow path.
 12. The system of claim 7 wherein the smoothdeposited film has a surface roughness less than the electromagneticskin-depth of the RF cavity resulting in reduced surface resistivity andhigher cavity Q.
 13. The system of claim 1 further configured with analignment jig that is used to hold a vane, of multiple vanes of an RFaccelerator, at a fixed position on an inner surface of the RFaccelerator cavity during operation of the system to carry out themethod for nanolayering a surface of a three-dimensional surface. 14.The system of claim 13 wherein the alignment jig is configured tomaintain intra-vane dimensional tolerances, vane gap spacing, vanealignment and beam positioning during fixturing and bonding within theRF accelerator cavity, including utilizing measurement locations,sensors and diagnostic ports for the precision alignment andcharacterization of the vane spacing and electromagnetic properties. 15.The system of claim 1 wherein the method for nanolayering, whencompleted, results in physical fixed attachment of the vane to the innersurface of the RF accelerator cavity.
 16. The system of claim 1 whereinone or more of surfaces covered by the sputter target material duringoperation of the system comprises a material having material propertiesthat differ from material properties of the sputter target material. 17.The system of claim 1 wherein the system is configured to provide thesputter target material on a surface of a vane tip of a vane positionedwithin the RF accelerator cavity, thereby resulting in a treated surfaceof the RF accelerator cavity having at least one property of the groupof properties consisting of: higher field emission limits, lowersecondary electron emission, reduced surface atom mobility, highunscreened plasma potential, low electron density, low surfaceroughness, and high work function.
 18. The system of claim 1 wherein thesystem is configured to provide the sputter target material on a surfacewithin the RF accelerator cavity resulting in an RF accelerator having adirect coupled RF from high-Q structures resulting in one or moreenhanced performance characteristics taken from the group consisting of:lowered power required for acceleration, and a higher permitted fieldgradient within the RF accelerator cavity.
 19. A method for carryingout, by a system, a nanolaying of a surface of a three-dimensionalsurface of an RF accelerator cavity and associated superconductingcavities by generating and controlling ion flux for direct currenthigh-power impulse magnetron sputtering, wherein the system comprises: amagnetic array comprising multiple sets of magnets arranged to haveHall-Effect regions that run lengthwise along a sputter target; and anelongated sputtering electrode material tube surrounding the magneticarray comprising multiple sets of magnets arranged to have Hall-Effectregions that that run lengthwise along the sputter target, and whereinthe method comprises: providing a vacuum apparatus containing asputtering magnetron target electrode; generating a high-power pulsedplasma magnetron discharge with a high-current negative direct current(DC) pulse to the sputtering magnetron target electrode; and generatinga configurable sustained positive voltage kick pulse to the magnetrontarget electrode after terminating the negative DC pulse, wherein duringthe generating, program processor configured logic circuitry issues acontrol signal to control at least one kick pulse property of thesustained positive voltage kick pulse taken from the group consistingof: onset delay, duration, amplitude and frequency including modulationthereof.
 20. The method of claim 19 wherein the generating aconfigurable sustained positive voltage kick pulse is carried out usinga capacitive stored power source and a positive pulse power transistor,and wherein the control signal is issued, during the generating, to thepositive pulse power transistor.